A question about GtkPaned

I'm using the last gtk2 version on window
the GtkHpaned or GtkVpaned has no  drag button in the center of separation bar
how you can see in the manual, all the border is grey ,
 is possible to drag it anyway, but a user may be
disoriented, it is not possible to understand that there is a panel on left or right side if one of this is closed.

Strange !!!


Thanks